1. Field of the Invention
The present invention relates to a fuel cell having a tank for storage of hydrogen generated, and more particularly, to a fuel cell having a hydrogen storage tank, the fuel cell storing hydrogen generated from a chemical reaction and generating electricity using the stored hydrogen without a separate external heat source.
2. Description of the Related Art
With recent increased use of portable small-sized electronic devices such as mobile phones, personal digital assistants, digital cameras, notebook computers and the like and especially with introduction of digital multimedia broadcasting, small-sized mobile terminals are required to have a power source with improved capability.
Having a capacity equivalent to about two-hour viewing of digital multimedia broadcasting, the generally used lithium ion secondary batteries are undergoing efforts to improve their capacity. However, there has been rising expectation for a fuel cell with further miniaturized size and higher capacity of power for a more fundamental solution.
In general, a fuel cell directly converts chemical energy, generated by oxidizing fuel, to electric energy, which is similar to a general chemical battery in that the principle of oxidation and reduction reaction is utilized. However, there is also a difference in that reactants are continuously supplied into a closed system and continuously exhausted out of the system in the fuel cell unlike a chemical battery in which cell reaction takes place only inside a system.
Known methods of embodying such a fuel cell include a direct methanol method in which hydrocarbon fuel such as methanol is directly supplied to a fuel electrode and a reformed hydrogen fuel cell (RHFC) method in which hydrogen is extracted from methanol and injected into a fuel electrode. The RHFC method uses hydrogen for fuel as in a polymer electrode membrane (PEM) method, which is advantageous in terms of high output, high electric capacity per unit volume and no other reactants besides water, but requires a separate reformer and thus is disadvantageous in terms of miniaturization.
In order for the fuel cell to obtain high power output density, a reformer for converting liquid fuel to gas fuel like hydrogen is required. The reformer includes an evaporating part for gasifying hydrocarbon liquid fuel, a reforming part for converting methanol into hydrogen at 250 to 350° C. through a catalytic reaction, and one of a CO removing part and CO2 removing part for removing byproducts additionally generated during the reforming reaction, i.e., CO gas or CO2 gas.
However, since the reforming reaction entails a heat absorption reaction taking place at a temperature maintained in a range of 250 to 350° C. in the reforming part and heat generation reaction taking place at a temperature maintained in a range of 170 to 200° C. in the CO removing part, a high-temperature system with a complex structure is required for high reaction efficiency. Therefore, the fuel cell has a complicated structure with limitations in reducing the manufacturing costs.
In addition, a separate structure for removing the byproducts generated during the reforming reaction, i.e., CO gas or CO2 gas is required, which limits reduction of the total volume and manufacturing costs of the fuel cell.
International patent publication WO 02/08118 discloses a technology in which a fuel cartridge including caustic soda and aluminum in a container filled with a certain amount of water is disposed to allow hydrolysis of water and aluminum with high-density caustic soda as a catalyst, thereby generating a hydrolysate Al(OH)3 and hydrogen H2 as in following equation 1. The hydrolysate Al(OH)3 bonds with oxygen to become Al2O3 and adheres to aluminum but is separated from the aluminum by caustic soda, thereby allowing continuous hydrolytic reactions accompanying heat generation as hydrogen generated in the container is supplied to a burner through a pipe and used as a fuel for the burner.2Al+6H2O→2Al(OH)3+3H2 (catalyst: NaOH)  Equation 1
However, since the conventional technology requires injecting high density of caustic soda, which is difficult to handle, it is cumbersome and biologically harmful to handle and use the fuel cell.
In addition, when the container placed vertically becomes inclined in a certain angle, the level of water filled in the container is changed and the fuel cartridge is exposed out of the water. This may significantly decrease the amount of hydrogen or stop the hydrogen generation from the reaction of formula 1. Thus, the container should be maintained vertically to have the fuel cartridge immersed in the water at all time, which renders cumbersome handling and use.
Furthermore, since the amount of hydrogen generated from the container is not constant per time, the conventional technology is limited in supplying the hydrogen generated from the container and in stably generating electricity.